1. Field of the Invention
The present invention is related generally to the field of orthodontics. More particularly, the present invention is related to improved dental appliances and systems, and methods for using and making the same.
Elastic positioners optionally in combination with attachments to the patient""s teeth are employed in orthodontic treatments for controlled tooth movement to a predetermined position. In providing such appliances and treatments, it is important to move teeth to an ideal pre-determined position with gentle controlled forces. Typically, the appliance is fabricated to provide accuracy of placement in compliance with the exact shape of the teeth or the exact shape and placement of the attachment device.
The use of elastic positioners for repositioning teeth is known. Such elastic positioners comprise a thin shell of elastic material that generally conforms to a patient""s teeth but is slightly out of alignment with the initial tooth configuration. By properly choosing the configuration, placement of the elastic positioner over the teeth will move individual teeth to desired intermediate or final positions over time. Of particular interest to the present invention, a system comprising multiple elastic tooth positioning appliances for performing orthodontic procedures is described in published PCT application WO98/58596 which corresponds to co-pending application Ser. No. 08/947,080, assigned to the assignee of the present application.
The resilient repositioning forces required to move a tooth from one position to another position in a reasonable amount of time may be formidable. The design of appliances capable of imparting such forces with acceptable comfort and appearance has been a challenge. To achieve such forces, the appliance must be relatively stiff (i.e. possess a high strength or high modulus) to provide a sufficient grip on the teeth. The stiffness both ensures that the dental appliance remains firmly in position on the patient""s teeth and provides the repositioning force necessary to move the teeth. The stiffness also permits the dental appliance to xe2x80x9cgrab holdxe2x80x9d of an anchor device or other surface feature which may be present on the tooth to apply a directed force to execute orthodontic tooth movements.
While appliance stiffness is desirable for providing repositioning forces and for maintaining appliance position on the teeth, the removal of stiff appliances can be difficult. Tooth positioners which are stiff and tightly conform to the teeth can require the use of orthodontic tools for removal, making removal by the patient very difficult. Periodic removal is desirable for a number of purposes including cleaning, dental hygiene, removal before meals, removal for cosmetic purposes, and removal and replacement in the course of treatment. In most or all of these cases, however, it will be inconvenient for the patient to visit the practitioner. Moreover, the use of tools can damage the appliance, making its reuse difficult or impossible.
For these reasons, it would be desirable to provide alternative methods, appliance designs, and systems for removing a dental appliance from the teeth. Such methods and apparatus, systems should be economical and, in particular, should reduce the difficulty experienced and the amount of time required by the practitioner and/or patient in removing and subsequently re-applying the appliance. At least some of these objectives will be met by the methods and systems of the present invention described hereinafter.
2. Description of the Background Art
WO98/5896 and co-pending application Ser. No. 08/947,080 are referenced above. Tooth positioners for finishing orthodontic treatment are described by Kesling in the Am. J. Orthod. Oral. Surg. 31:297-304 (1945) and 32:285-293 (1946). The use of silicone positioners for the comprehensive orthodontic realignment of a patient""s teeth is described in Warunek et al. (1989) J. Clin. Orthod. 23:694-700. Clear plastic retainers for finishing and maintaining tooth positions are commercially available from Raintree Essix, Inc., New Orleans, La. 70125, and Tru-Tain Plastics, Rochester, Minn. 55902. The manufacture of orthodontic positioners is described in U.S. Pat. Nos. 5,186,623; 5,059,118; 5,055,039; 5,035,613; 4,856,991; 4,798,534; and 4,755,139.
Other publications describing the fabrication and use of dental positioners include Kleemann and Janssen (1996) J. Clin. Orthodon. 30:673-680; Cureton (1996) J. Clin. Orthodon. 30:390-395; Chiappone (1980) J. Clin. Orthodon. 14:121-133; Shilliday (1971) Am. J. Orthodontics 59:596-599; Wells (1970) Am. J. Orthodontics 58:351-366; and Cottingham (1969) Am. J. Orthodontics 55 23-31.
The present invention provides improved dental appliances and methods for using and fabricating such appliances. Individual appliances comprise a polymeric shell having a teeth-receiving cavity formed therein. The shell will have the necessary stiffness to firmly secure the appliance on the teeth and provide controlled forces required for repositioning the teeth. As discussed in detail below, one or more removal features or mechanisms will be provided to facilitate removal of the appliances from the teeth. The removal mechanism may be an integral property or characteristic of the shell and/or may be a separate component or components in addition to the shell. Exemplary shell properties include changes in stiffness or shape induced by exposure of the shell to different environmental conditions, e.g. a change in temperature, a change in pH, a change in ionic strength, or the like. Exemplary additional components include adhesives, interface layers (between the shell and the tooth), tooth anchors, reinforcement components (layers, filaments, braids, etc.), where such components can change stiffness, dimensions, orientations, or the like to selectively hold or release the shell onto the teeth. Usually, the changes in the additional components will be induced by the same types of environmental changes used for inducing property changes in the shell. Alternatively, removal mechanisms comprising separate components could be stimulated by exposure to an external energy source, e.g. being mechanically, electrically, optically, magnetically or otherwise triggered to induce a change which causes or permits release of the shell from the teeth.
Use of such removal mechanisms is advantageous in a number of respects. Environmental changes can be easily implanted by a practitioner or patient. For example, the practitioner or patient can wash the mouth with an appropriately heated, pH-modified, ionic strength controlled, or other solution which can induce the desired change in the removal mechanism. While the use of mechanically, electrically, or optically triggered removal mechanisms may require additional equipment, such mechanisms can also be very simple and suitable for use by the patient as well as the practitioner. In all cases, the removal mechanisms can usually be made reversible, i.e. the appliance can be xe2x80x9cswitchablexe2x80x9d between attached configurations where the appliance will remain in place on the teeth and a release configuration where the appliance can be removed form the teeth. This is a particular advantage since is allows the appliance to be temporarily xe2x80x9creconfiguredxe2x80x9d and removed for any purpose and then repositioned over the teeth to continue the treatment.
In a first aspect of the invention, a state change reduces the stiffness or shape (or both) of the shell material such that the engagement forces between the shell and the teeth or other interfaces are reduced or eliminated. The state change can be a change in any material property which affects stiffness or shape, such as hardness/softness (as measured by durometer), elasticity, phase (as with shape memory polymers and materials), or the like. Preferably, the state change will be reversible so that the shell can recapture the stiffness lost or recover the shape which was lost while undergoing the initial state change. The reduction of stiffness will usually comprise a softening and/or increasing elasticity of the shell material, permitting the shell to become more easily pulled from over the teeth. A change in shape will reduce or eliminate engagement forces between the appliance and the teeth or other interfaces due to an expansion, contraction, partial opening, reduction of interference, or other reconfiguration of the appliance. The desired state change will preferably be induced by an environmental change which can easily be effected in the patient""s mouth. Preferred environmental changes are these which can be implemented by a simple mouth wash with a solution having a particular composition, pH, temperature, ionic strength or other property. The selected property should be one that the patient will not normally encounter in daily life, at least during periods when release of the appliance is not intended. For example, temperature would not be a good choice unless it is intended that the appliance be removed when eating or drinking hot foods and drinks. The property should also be one that is physiologically acceptable, e.g. very high or very low pH might not be desirable.
It is not necessary, however, that the xe2x80x9creleasedxe2x80x9d configuration be long term or sustainable. In many instances, the removal mechanism will permit mounting of the appliance onto the teeth when the removal mechanism is in its xe2x80x9cattachedxe2x80x9d configuration. To remove the appliance, the released configuration need be sustained only long enough to complete the removal. The removal mechanism can then revert to the attached configuration, as the result of for example, cooling, pH change, and ionic strength change, and still be replaced over the teeth without the need to restore the released configuration.
In one embodiment, the removal mechanism may be an integral property of the appliance, usually being an inherent property of the shell or a part of the shell. An orthodontic appliance is provided which has a shell formed of at least one layer of a polymeric material. The shell has a cavity which fits closely over a contiguous group of teeth. A contiguous group of teeth includes at least 3 teeth, but usually 4 or more. The at least one-layer of polymeric material has a first state where the appliance is held onto the teeth and a second state where the appliance may be removed from the teeth. The first state will exist when the shell is in place in the patient""s mouth in the absence of any xe2x80x9cnon-oralxe2x80x9d conditions or externally applied energy or other stimuli. The second state can then be selectively induced by creating a xe2x80x9cnon-oralxe2x80x9d environment in the patient""s mouth, as discussed above. The non-oral environment may consist of a non-physiological temperature ( above 37xc2x0 C., preferably 40-55xc2x0 C.; or below 37xc2x0 C., preferably below 30xc2x0 C. a non-physiologic pH (above 8, preferably above 9, more preferably above 8.5 or below 7, preferably below 6, more preferably below 6.5), a non-physiologic ionic strength, such as 3% sodium chloride, or the like.
In another embodiment, the removal mechanism is formed as one or more additional component(s) or mechanism(s). Such systems will include at least one polymeric shell which can be removably placed over a patient""s teeth. The separate removal component or mechanism is switchable from a first state to a second state.
In yet another embodiment, a dental appliance system will include a dental appliance, which has a shell with a cavity. The system will further include an attachment device which is formed or exists separately from the shell. The attachment device is usually configured to be positioned between the outer surface of the teeth and an inner surface of the cavity. The device is switchable between a first state, where the appliance is held onto the teeth, and a second state, where the appliance may be removed from the teeth. The switch is stimulated or made to occur as a response to an environmental change.
In another aspect of the invention, an improved method is provided for removing an appliance from the teeth. Preferably, the appliance is a polymeric shell, which has cavities shaped to receive and resiliently reposition teeth to produce a final tooth arrangement. In a first aspect, the improvement comprises transforming the shell from a first state, where the appliance is held onto the teeth, to a second state where the appliance may be removed from the teeth. The transformation is performed in situ in the patient""s mouth, usually the exposure to an environmental change or external stimulus as described above. The transformation is repeatable so that the appliance can be reinserted.
In another aspect a method for fabricating a removable incremental tooth position adjustment appliance is provided including forming a shell of at least one layer of a polymeric material with a teeth mold. The shell is formed with cavities shaped to receive and resiliently reposition teeth from one arrangement to a successive arrangement. The shell transforms from a first state, where the appliance is held onto the teeth, to a second state, where the appliance may be released from the teeth.
In another aspect, an appliance system comprises a plurality of individual appliances that can be used for repositioning teeth from an initial tooth arrangement to a final tooth arrangement using a plurality of dental incremental position adjustment appliances. In this embodiment, the plurality of position adjustment appliances will include a first appliance having a geometry selected to reposition the teeth from the initial tooth arrangement to a first intermediate arrangement. The plurality of position adjustment appliances will also have one or more intermediate appliances having geometries selected to progressively reposition the teeth from the first intermediate arrangement to successive intermediate arrangements. The position adjustment appliances will still further have a final appliance having a geometry selected to progressively reposition the teeth from the last intermediate arrangement to the final tooth arrangement. The system will also include a removal mechanism formed into each adjustment appliance described above. The removal mechanism transforms from a first state to a second state to release each appliance from the teeth. In a preferred embodiment, the transformation is activated by a stimulus, preferably an environmental stimulus or condition.